1. Field of the Invention
The present invention relates to data storage units, and especially to data migration, and, in particular, to a method and a storage unit to control hierarchical management of data migration to maintain balanced performance.
2. Description of the Prior Art
In a conventional hierarchical control system, such as disclosed in JP-A-9-44381, a controller executes migration of frequently accessed data to a storage unit having a high access speed and transfers infrequently accessed data to a storage unit having a low access speed, based on access frequency of data managed inside the controller.
In a typically Storage Area Network (SAN) system, a plurality of applications in one or more host units share volume groups, and the volume groups to which the applications on the host units execute input and output extend over two or more controllers. Conventional hierarchical control system assigns volumes to a high-speed storage pool in a hierarchical sequence of reference values that reflect how frequently the volumes have been accessed, based on the activity rate of the volumes in a unit of controllers. The higher the reference value the higher the access activity.
Therefore, if a volume has a higher reference value than that of a volume for a specific application under the same controller, transfer of the higher reference value volume precedes transfer of the application volume. As a result, there may be times when a performance bottleneck of a specific application cannot be resolved. That is, sometimes data migrations that do not contribute to improved performance are executed, whereas data migrations that would contribute to improved performance are not executed.
In addition, because the controllers cannot share information about the data migration priorities assigned, data migration of a volume accessed by a specific application cannot be preceded. A conventional hierarchical control system assigns volumes to a high-speed storage pool in descending order of their reference values, which are based on the number of times the volumes have been accessed over a specified period.
Some applications show quite different accessing patterns depending on timing requirements. However, the difficulty of discriminating between volumes having a continual high activity rate and volumes causing a large performance bottleneck because of accessing concentrated at a specific time, but which have a low activity rate over a long period, results in inefficiency in executing transfer of the volumes in the absence of data migration. This problem can be avoided by acquiring and storing access data at very short intervals; however, data acquisition at very short intervals in a disk array controller increases the controller load, disturbing the load equilibrium and impairing the performance of the total system.
Software has been developed for acquiring volume information at short intervals without increasing the total system load. The software stores and displays such access data as activity rates of the volumes communicating with the controller. However, this software, by itself, cannot acquire the corresponding structures of logical volumes and physical drives, the activity rates of the physical drives, volume performance limitations depending on accessing modes, etc., all of which are necessary for hierarchical management control. Nor can the software automatically instruct the controller about migration. Consequently, the software cannot plan data migration to precisely equilibrate the load to the total system.
One objective of the present invention is to provide a more efficient system to execute data migration and a method thereof, when volumes of the same application extend over two or more controllers. Another objective is to provide a system for executing migration of a volume of a specific application having priority and a method thereof, when the volumes of the same application extend over two or more controllers. Yet another objective of the present invention is to provide a system for acquiring volume information over short intervals without increasing the load on the total system, and for automatically instructing the controller to execute migration and a method thereof.
A storage system configured to extend over two or more controllers accessed by two or more applications on host unit communicates with two or more controllers and is provided with a means (external manager, etc.) having the functions of gathering, compiling and managing the activity rate of each physical drive constituting logical volumes, the activity rate of the logical volumes, the access patterns, the performance information and the configuration information of the correlation between the physical drives and the logical volumes.
The external manager generates a data migration instruction by using the accumulated information; and inputs the application priority conditions and a priority period to equilibrate the accessing load, and issues an instruction to the controller. Because the external manager treats all performance bottlenecked volumes of the highest priority application as migration targets, performance efficiency can be improved by data migration of the volume group most frequently accessed by a specific application disk array unit groups accessed by two or more applications. Further, since the external manager does not execute migration of an application whose performance cannot be improved by data migration because the performance bottleneck of a portion of the volumes cannot be resolved, the resources of a high speed storage pool are not needlessly consumed and greater performance efficiency is enabled.